[REF] Simplify a couple of variables

Rather than rely on these being passed around retrieve them with
a consistent function.

Note tax_amount is retrieved one other place but that is fixed in
civicrm#19757

Line item will be used less once
civicrm#19801 is merged

CRM/Member/Form/Membership.php

@@ -1219,14 +1219,14 @@ public function submit(): void {
           $paymentParams,
           [
             'contact_id' => $this->_contributorContactID,
-            'line_item' => $lineItem,
+            'line_item' => [$this->order->getPriceSetID() => $this->order->getLineItems()],
             'is_test' => $this->isTest(),
             'campaign_id' => $paymentParams['campaign_id'] ?? NULL,
             'source' => CRM_Utils_Array::value('source', $paymentParams, CRM_Utils_Array::value('description', $paymentParams)),
             'payment_instrument_id' => $this->getPaymentInstrumentID(),
             'financial_type_id' => $this->getFinancialTypeID(),
             'receive_date' => CRM_Utils_Time::date('YmdHis'),
-            'tax_amount' => $params['tax_amount'] ?? NULL,
+            'tax_amount' => $this->order->getTotalTaxAmount(),
             'total_amount' => $this->order->getTotalAmount(),
             'invoice_id' => $this->getInvoiceID(),
             'currency' => $this->getCurrency(),